Comparison of the trabecular architecture and the isostatic stress flow in the human calcaneus.

It is a common theory that the architecture of trabecular bone follows the principal stress trajectories, as suggested by Wolff's pioneering studies of the proximal femur. Since first published in the late 19th-century, this observation (popularized as "Wolff's law") has been supported by numerous studies, but nearly all of them have been focused on the femoral head and neck. In this study, the manifestation of Wolff's law in the human calcaneus has been analyzed. For this purpose, finite element (FE) analysis of the entire complex of the foot during standing was undertaken. Orientation of the principal stress flow through the calcaneus was compared with the trabecular alignment in a single cadaveric calcaneal specimen, by fitting second-order polynomials to real trabecular paths and FE-predicted isostatics and calculating their angle of inclination with the calcaneal cortex at their insertion points. Four dominant trabecular patterns were identified in the cadaveric sagittal section of the specimen of the calcaneus: one directed primarily in the dorsal-plantar direction, one aligned anteriorly-posteriorly, and two that are strongly oblique. Subsequent numerical simulations showed that the dorsal-plantar oriented and posterior oblique trabecular paths are aimed to support compressive stresses, while the antero-posteriorly directed and anterior oblique groups act to bear tension. Insertion angles of real trabecular paths into the calcaneal cortex were similar to those of the isostatics that were computed under musculoskeletal loading conditions of standing (maximum absolute local difference 13 degrees, maximum local error 60%). This suggests that the trabecular patterns of the calcaneus are mainly shaped by isostatics (static principal stress flow) that are characteristic of the standing posture. The present modeling approach can be utilized to explore effects of abnormal alterations in the isostatic flow on the microarchitecture of the calcaneal trabeculae, as well as for better understanding of the mechanisms of calcaneal fractures.

Loading conditions and bone formation in the GH region of the shoulder.

The present study investigates how loading of the shoulder effect the formation of the trabeculae in the subarticular region of the gleno-humeral joint. Bone morphology was determined from scapular cadaveric specimens and finite element (FE) analysis was employed to analyse principal stress trajectories. Boundary conditions corresponded to five functional activities were considered. The results show deviations of the computed trajectories from actual trabecular lines obtained from the bone specimens ranged on average from 10% to 17%. Each activity produced different regional deviation corresponding to the specific loading condition. This study concludes that certain loading conditions are more significant in explaining the formation of the trabecular architecture. The results also suggest that due to the extra sensitivity of the front and the rear aspects of the "lateral region" to the loading conditions, these regions may be more indicative in reflecting shoulder injuries.

Towards the control of a powered orthosis for people with muscular dystrophy.

The paper describes the development of a passive/active orthosis for people with limited anti-gravity strength in their arms. This is symptomatic of conditions such as muscular dystrophy and spinal muscular atrophy. A passive orthosis was designed and developed using linear elastic elements. The system is being tested with children with disabilities and preliminary results are encouraging. An RT200 robot was also used as a test-bed for an active orthosis. The robot was instrumented with a six-axis force/torque sensor at the end-effector. The force acted as the input to the robot. The robot kinematics and dynamics were modelled. A number of control schemes were implemented on the test-bed including force proportional to velocity and acceleration; these schemes were evaluated with two subjects.

Analysis of arm trajectories of everyday tasks for the development of an upper-limb orthosis.

Spatiotemporal arm and body movements of able-bodied subjects performing nine everyday tasks were recorded for the purpose of guiding the development of an upper-limb orthosis. To provide a user the opportunity to carry out these tasks with natural movements, the orthosis should allow replication of the measured trajectories. We outline the orthosis architecture, which supports the user's upper arm and forearm, and analyze the movement data to obtain orthosis design specifications. Trajectories were obtained using six-degree-of-freedom magnetic position sensors affixed to the wrist, elbow, shoulder, trunk and head. Elbow trajectory data were decomposed into ranges along the principle Cartesian axes to provide a generally useful envelope measure. The smallest Cartesian parallel-piped that contained the elbow trajectories for most tasks was approximately 30 cm front/back, 15 cm side/side, and 17 cm up/down. A rough lower bound estimate obtained by asking subjects to repeat the tasks while minimizing elbow movement substantially reduced movement in the up/down and side/side dimensions. Elbow angles were generally in the range 50 degrees-150 degrees, and the angle of the forearm with respect to vertical was 10 degrees-110 degrees. Raw trajectory data may be downloaded from www://asel.udel.edu/robotics/orthosis/range.h tml.

Evaluation of an isometric and a position joystick in a target acquisition task for individuals with cerebral palsy.

Individuals with cerebral palsy (CP) with upper limb disability have difficulty operating standard computer input devices such as, a mouse and a keyboard. The present study evaluated the performance of unimpaired individuals and those with CP in the use of a zero-order spring-centered position joystick and a zero-order isometric joystick when interacting with the computer. We hypothesize that the isometric device due to its stiff resistance would provide better control on cursor movement than the position joystick. The subjects acquired differently sized targets at different distances by positioning a cursor on the target. Performance with the position joystick was superior to that of the isometric joystick. The time to acquire the target was directly proportional to the cursor-target distance A, and indirectly proportional to the target size W. Subjects chose to move more slowly toward the smaller and closer targets and they increased speed for larger and more distant targets. The phase-plane diagram that plots values of the velocity profile of the cursor over its displacement revealed the presence of one large amplitude movement that accounts for the peak velocity of the cursor, and several submovements. Fitts' index of difficulty, log(e)(2W/A) was found to be a good predictor of the movement time in a cursor positioning task for both, unimpaired individuals and those with CP.

A body-powered functional upper limb orthosis.

This paper describes the development and preliminary testing of a functional upper-limb orthosis for people that have limited strength in their arms. This is symptomatic of conditions such as muscular dystrophy (MD), spinal muscular atrophy (SMA), and partial spinal cord injury. The exoskeletal orthosis is wheelchair mounted, has two links and four degrees of freedom. It uses linear elastic elements to balance out the effects of gravity in three dimensions. Preliminary results on testing with ten subjects will be presented.

A study of shoulder motions as a control source for adolescents with C4 level SCI.

This study quantitatively examined and compared the shoulder motions of C4 level spinal cord injury (SCI), C5 level SCI, and able-bodied persons as a command source. The study was motivated by both the success of shoulder control in functional electrical stimulation (FES) systems designed for C5 level SCI people and the lack of quantitative information on the shoulder motion of persons with C4 level SCI. A dual-axis transducer was used to monitor the elevation/depression and protraction/retraction angles of each subject's shoulder while they performed three experimental sections which examined: the range of active shoulder motion; the ability to move incrementally to discrete positions with the aid of visual feedback; and the ability to hold discrete shoulder positions for an extended period without visual feedback. Results indicated that each group had the largest average shoulder displacements (abled = 23 degrees +/- 4 degrees, C5's = 14 degrees +/- 3 degrees, and C4's = 9 degrees +/- 3 degrees) while attempting to elevate and that on average the C4 group had the smallest range of active shoulder motion. No statistically significant differences between the groups were found in either the accuracy or stability of reaching discrete positions with the aid of visual feedback or in the accuracy of holding discrete shoulder positions for an extended period without visual feedback. The results suggest that within their limited range of motion the individuals with C4 level SCI retained shoulder control sufficient for use as an neuroprosthetic command interface.

Emergency care in patients wearing body casts.

OBJECTIVE: To describe a body cast modification that allows rapid chest exposure for cardiopulmonary resuscitation and alert the medical community to the 3% to 5% incidence of cardiopulmonary arrest in the hospital while wearing such a cast. DESIGN. Single trial timed cast cutting, multiple trial cast shell loading, and clinical observations of perforated casts for cracking or breakage. SETTING: University hospital castroom, mechanical engineering laboratory. INTERVENTION: Body casts mounted on a life-sized torso mold were perforated at 2-inch (50 mm), 1-inch (25 mm), or 1/2 inch (12 mm) intervals around the chest with a 12-mm-diameter vibrating drill. Using a cast saw, the chest piece of each body cast was removed and the time recorded. Engineering studies were performed on two cast shells with and without 12-mm-wide holes up to 1/2" (12 mm) apart, loading the fiberglass to the point of failure and recording the data. Body casts with 1" (25 mm)-interval holes worn by 40 patients were examined after 12 weeks for evidence of failure. MAIN OUTCOME MEASURES: Chest piece removal times of body cast shells with and without holes were compared. Loading data of cast shells were compared to determine if holes as close as 1/2" (12 mm) significantly weakened the cast. Forty casts, perforated at 1-inch (25 mm) intervals, were observed for failure after 12 weeks of wear. RESULTS: Chest exposure time of a mold encased in a fiberglass cast was reduced from 1 minute to 15 seconds; plaster cast removal was reduced from 3 minutes to 1 minute. Engineering studies of perforated casts showed no significant decrease in strength. Casts with and without holes could support chest forces of up to 330 pounds. No failure was observed in casts with perforations 1 inch (25 mm) apart worn for 12 weeks. CONCLUSION: Perforated body casts reduced removal time to 15 seconds without weakening of the cast and provide lifesaving time to perform effective CPR.

Characterization of human joint impedance during impulsive motion.

The objective of the present work is to make use of the limited existing information on human joint impedance and to supplement and refine it synthetically, by means of simulation. A modular concept was applied to the construction of a joint model. The basic module was an individual revolute joint which was constrained by four resistive elements. The module was adapted to represent the different anatomical joints by specifying their corresponding mechanical parameters. The modular joint model was tested by incorporating it into a two dimensional whole body model and subjecting it to known impulsive conditions such as those reported in literature with regard to vehicular collision. Fine tuning was done by examining the sensitivity of the human model kinematic response to variation of the joint parameters. The whole body model was simulated with the aid of the ADAMS computer code. A comparison of the existing experimental data related to the sled test performed on a Hybrid III dummy with synthetic collision results showed good agreement.

Alignment procedure for the optimal fitting of lower limb prostheses.

Systematic methods for optimizing the fitting and alignment of artificial legs were developed in this study. The procedures were based on gait analysis and included the following aspects: stump-prosthesis interface or socket geometry, the selection of components from which the artificial leg was constructed, and dynamic alignment of the prosthesis. The amputee's adaptation to deliberately imposed perturbations in his prosthesis, and the resulting compensatory mechanisms are also discussed.

Biomechanical evaluation of an adjustable patellar tendon bearing prosthesis.

The purpose of this study was to determine the relation between geometry of the patellar tendon (PT) insertion in the socket and the dynamic load transmitted through the PT, in a patellar tendon bearing (PTB) prosthesis. The dynamic load was measured by a specially constructed two-component load cell, which was mounted on the experimental prosthesis. Geometry of the PT insertion relative to the socket was altered by adjusting the location of the mounting frame-load cell assembly. Evaluation of performance of the prosthesis in the range of geometries investigated was made objectively by gait analysis of the patients. The latter was performed on a 10 m walkpath, including at halfway two forceplates, from which the foot-ground forces were recorded. Simultaneously, the PT forces on the prosthesis, as sensed by the load cell were monitored. Computer processing of the data included full analysis of the force-trace and the determination of criteria for optimization of the PT insertion. The resulting criteria were those which expressed minimization of abnormalities in the foot-ground forces of each patient, such as vertical and braking forces and their timings. The complete optimization procedure, which was undertaken for two below-knee male amputees, indicated the correct positioning of the PT insertion, actually taken in the final fitting procedure of the socket of the prosthesis.

Simulation of human gait with the aid of a simple mechanical model.

A simple mechanical model was used in this study to simulate the stance phase of human locomotion. The model consists of a concentrated mass supported by two elastic and viscous straight legs. The model is provided with a set of initial conditions at the instant of "heel strike" and then continues to move due to its inertia and the action of gravity. The simulation results were compared with the corresponding experimental data and have shown agreeable similarity. The model was also used to study the effect of some body features on the resulting walking pattern and to explain the generation of the ground reaction force characteristics.

End-bearing characteristics of patellar-tendon-bearing prosthesis--a preliminary report.

The present work was aimed at investigating the degree of participation of the stump end in the weightbearing process in PTB prostheses. Despite the belief that the stump end is not capable of withstanding high loads, it was revealed that most patients can bear from 15 percent up to 45 percent and more of their weight on the stump end. The limited number of patients studied diminishes the statistical significance, but the results of this work do suggest that the weightbearing mechanism of a PTB prosthesis can be further improved by transferring more load through the stump end. It is suggested that a nondestructive technique for assessing the end-bearing efficiency of the prosthesis be developed. Also, the criteria for design of the socket end in order to produce the desired load-bearing features needs further investigation.

Dynamic features of standing and their correlation with neurological disorders.

Standing posture is a result of complex activity of the human control system. Irregularities of postural control may be expected to result in deviations from normal standing. In the present study a ballistic monitoring technique was employed to establish criteria for assessment of postural disorders. Two "Kistler" force plate dynamometers were used to measure changes in the weight bearing components of each foot and displacement of the center of pressure of each foot. The patterns were analysed separately, and it was found that each of the monitored parameters demonstrated three modes of oscillation--termed Tremor, Ataxia and Sway. Statistical analysis conducted on three groups of subjects (normals, post-C.V.A. hemiplegics and brain injured) revealed significant intergroup differences in movement patterns. Good agreement was found between the interpretation of the ballistic features and the clinical diagnosis.

Effects of lower body negative pressure (LBNP) on the distribution of body fluids.

Reduction of pressure on the lower part of the human body is believed to be capable of altering the normal fluid distribution. This could serve as a therapeutic method for emergency relief of the effects of hypertension, or it could be used as counterbalance for zero gravity and assist in preparing astronauts for reentry into the gravitational field. The present work describes a technique of assessment of the fluid shift caused by such pressure reduction. Thirty experiments were performed on four healthy subjects. The shift of fluid was assessed by measuring changes in body weight distribution of the tested subjects. The shift of fluid was assessed by measuring changes in body weight distribution of the tested subjects. The experimental results show that two processes may have taken place within the human body: shift of blood within the vascular system and diffusion of fluids from the circulatory system to the tissues. The total fluid shift ranges between 1 and 2 kg. It was proportional to the pressure gradient and exponential with time. The systolic blood pressure was reduced with the pressure reduction while the pulse rate increased.

A kneeless leg prothesis for the elderly amputee, advanced version.

The work described in this paper is part of a development and evaluation program, the aim of which was to bring a telescopic kneeless leg prosthesis to a reliable, commercially viable, and easily manufacturable stage. It is considered that these aims have been almost achieved, as the prosthesis appears to improve the gait characteristics significantly, compared with its first prototypes and compared with the conventional National Health Service (N.H.S.) above-knee prostheses. The clinical evaluation was carried out with three patients and its results were found satisfactory. The specific advantages of this prosthesis compared with the conventional prostheses are: improved proprioception and stability, and improvements of certain kinematic characteristics. The paper describes briefly the modified version of the prosthesis an the investigations undertaken, and also discusses the results obtained.